US Patent 10899942 Process for producing a coated pipe

The present invention deals with a process for producing a coated pipe. The process comprises (i) homopolymerising ethylene or copolymerising ethylene and an α-olefin comonomer in a first polymerisation step in the presence of a polymerisation catalyst to produce a first ethylene homo- or copolymer having a density of from 940 to 980 kg/m3 and a melt flow rate MFR2 of from 1 to 2000 g/10 min; (ii) homopolymerising ethylene or copolymerising ethylene and an α-olefin comonomer in a second polymerisation step in the presence of a first ethylene homo- or copolymer to produce a first ethylene polymer mixture comprising the first ethylene homo- or copolymer and a second ethylene homo- or copolymer, said first ethylene polymer mixture having a density of from 940 to 980 kg/m3 and a melt flow rate MFR2 of from 10 to 2000 g/10 min; (iii) copolymerising ethylene and an α-olefin comonomer in a third polymerisation step in the presence of the first ethylene polymer mixture to produce a second ethylene polymer mixture comprising the first ethylene polymer mixture and a third ethylene copolymer, said second ethylene polymer mixture having a density of from 915 to 965 kg/m3, preferably from 930 to 955 kg/m3 and a melt flow rate MFR5 of from 0.2 to 10 g/10 min; (iv) providing a pipe having an outer surface layer; (v) applying a coating composition onto the pipe outer surface layer to form a top coat layer, wherein the coating composition comprises the second ethylene polymer mixture.